This application claims the priority of German application 101 16 926.4, filed Apr. 5, 2001.
This invention relates to a method for triggering a gas generator for an air bag in a motor vehicle having acceleration sensors, an air bag, a gas generator which supplies a filling medium for filling the air bag, and an air bag control unit. The air bag control unit evaluates a collision by evaluating signals of the acceleration sensors and, by way of a control signal, triggers the gas generator. A volume flow of the filling medium supplied by the gas generator during a filling operation is influenceable by the control signal.
For protection of vehicle occupants in the event of a collision, it is generally known to detect acceleration values by acceleration sensors at different points in the vehicle. By way of a control unit, as a function of the detected acceleration values, restraint devices, such as air bags and belt tightening devices, are triggered.
A method of triggering restraint devices is known from European Patent Document 0458796 B2. In this case, acceleration is measured and, from acceleration values, speed values are generated by integration. The speed values reflect the accident-caused speed reduction. As a criterion for triggering an air bag, a threshold value can be defined for the speed signal. This threshold value is changeable as a function of parameters which are detected during the collision.
Two-stage or multistage gas generators are known for filling an air bag. In such a case, ignition of a second stage takes place in a time-staggered manner after ignition of a first stage. In order to adapt the air bag filling operation to the seriousness of an accident, not all stages of the gas generator are necessarily ignited, or a time period between two ignition points in time is varied.
It is known from German Patent Document DE 19816989 A1 to evaluate the seriousness of an accident according to the amount and course of the accident-caused speed reduction. The speed reduction determined is illustrated in a so-called speed event space as a function of time. This speed event space is divided into several zones, and each zone is assigned in an unambiguous manner to an accident seriousness range. If the accident-caused speed reduction during a given time period takes place, for example, in zone I, then accident seriousness I is assigned to the accident and the triggering of the air bag gas generator provided for accident seriousness I is implemented. In order to be able to adapt the triggering of the gas generator to the seriousness of the accident, a two-stage gas generator is provided.
It is known from German Patent Document DE 19702259 C1 to have a gas generator by which the inflating speed and the inflating pressure can be better adapted to the seriousness of an accident than with a two-stage gas generator. A control element is provided for controlling outflow volume and outflow speed of the compressed gas. The control element can be actuated using a piezoelectric element by way of an amplifying mechanism. Gas flow can be controlled for filling an air bag by the continuous adjustability of the piezoelectric element.
A device for controlling a gas bag arrangement by which an inflating volume can be adapted to the seriousness of an accident after initiating inflation is also known from German Patent Document DE 19740020 A1. For this purpose, several gas generators are assigned to a one-part or multipart gas bag arrangement. Each of these gas generators can be ignited by an ignition signal. By selection of the gas generators to be ignited and their ignition sequence, the inflating characteristic and the inflating volume can be defined.
Another way of adapting the filling of an air bag to a detected seriousness of an accident is known from German Patent Document DE 19913095 A1. Inflating of the air bag is controlled by igniting several primer pellets successively and/or by changing the effective cross-section of a blow-off opening of a gas generator with a controllable valve. A portion of the filling medium for the air bag escapes through the blow-off opening into the environment, so that this air bag is filled less as the cross-section of the blow-off opening increases. An adaptation to the seriousness of an accident thereby can take place.
A two-stage gas generator is known from German Patent Document DE 19816989 A1. In this case, as a function of the seriousness of an accident, one of two stages is or both stages are ignited.
A control system for a vehicle occupant protection device, such as an occupant restraint system, is known from German Patent Document DE 43 32 880 A1. This control system detects vehicle deceleration for controlling the vehicle occupant protection device, and determines an average vehicle deceleration value and a standard value of deviation of the vehicle deceleration.
It is also considered to be known, for controlling the volume flow of the filling medium into the air bag, to control the opening cross-section for the filling medium for filling the air bag by a controllable valve. A control of the opening of the valve corresponds to an indirect control of the volume flow of the filling medium into the air bag.
As an alternative, for the purpose of controlling the volume flow of the filling medium into the air bag, the volume flow of a combustible into a combustion chamber can be controlled by a controllable valve. In the combustion chamber, the combustible generates the filling medium for filling the air bag. The generated volume of the outflowing filling medium depends on the volume of the combustible which is guided into the combustion chamber.
It is an object of the invention to improve triggering of a gas generator for filling an air bag in a motor vehicle. According to the invention, this object is achieved by a gas generator triggering method in which an air bag control unit evaluates a collision by evaluating signals of acceleration sensors and, by way of a control signal, triggers the gas generator so that a volume flow of the filling medium supplied by the gas generator during a filling operation is influenceable by the control signal. The control signal, as a function of evaluation of the collision, is changed several times between two conditions, and filling of the air bag is adapted to collision seriousness by way of repeated changes of the control signal.
A gas generator is triggered by an air bag control unit for filing an air bag. For this purpose, the air bag control unit receives acceleration signals of an acceleration sensor. When triggering is to occur, the control unit generates, by way of analysis of the acceleration signals, a control signal for triggering the gas generator. Triggering of the gas generator influences the volume flow of the filling medium from the gas generator into the air bag. According to the invention, the control signal for triggering the gas generator, as a function of the analysis of the impact, alternates several times between two conditions. As a result of the repeated change of the control signal, filling of the air bag is adapted to the seriousness of the collision. One advantage of the method according to the invention is that, by way of a simple binary triggering of the gas generator, the protective effect of the air bag for the occupants can be adapted to an accident situation.
The repeated change of the control signals between the two conditions may be a periodical change. In the case of a periodical change, triggering of the gas generator can take place by way of a timed signal.
As a further development of the method, the gas generator has an adjustable valve which can be adjusted into at least two adjusting conditions with a different opening cross-section. Triggering of the gas generator takes place such that the position of the valve alternates several times successively between two conditions. The characteristic of the repeated change between the two valve positions is decisive for filling the air bag. The characteristic of the repeated change of the valve positions is particularly affected by the time period during which a valve is in one of the two valve positions, respectively; by the time period which is required in order to control a valve from one valve position into the other valve position; and by the frequency at which the change of the valve positions takes place. A variation of the ratio of the dwell times of the valve in the two valve positions causes a change of the filling operation of the air bag. This method has the advantage that, by way of a simple valve, which can be controlled into two conditions, an adaptation of the mass flow rate to the detected seriousness of the accident can take place during filling of the air bag.
The adjustable valve can be arranged at the filling medium output of the gas generator in order to control the volume flow of the filling medium from the gas generator into the air bag. This has the advantage that the volume flow of the filling medium is controlled directly by the triggered valve.
In an alternative further development, in the case of a gas generator which generates the filling medium for the air bag in a combustion chamber, the triggered valve can control the volume flow of a reactant into the combustion chamber. This alternative further development has an advantage that the volume flow into the chamber is smaller and the valve may have a smaller construction. In addition, the pressure difference between the reactant storage chamber and the combustion chamber can be selected to be smaller than would be possible in the case of the pressure difference between the combustion chamber and the ambient pressure during the filling operation. As a result, the mechanical demands on the valve can be reduced.
In a further development of the process, the two valve adjustments are defined by xe2x80x9copenxe2x80x9d and xe2x80x9cclosedxe2x80x9d conditions, so that, in the xe2x80x9cclosedxe2x80x9d condition, no gas, or a negligible amount of gas, for filling the air bag flows through the valve, and in the other, xe2x80x9copenxe2x80x9d, condition, a defined amount of gas for filling the air bag flows through the valve. The acceleration signal is evaluated in a predetermined manner. It is an advantage of this further development that triggering of the gas generator is simple. The gas volume for filling the air bag can be defined only by the added-up time period in which the valve is in the xe2x80x9copenxe2x80x9d position. It is a prerequisite in this case that the time period for the opening operation and the closing operation of the valve be short in comparison to the time periods in which the valve is in the xe2x80x9copenxe2x80x9d and xe2x80x9cclosedxe2x80x9d positions. If this is not so, then the adjusting time of the valve should additionally be taken into account when determining the gas volume.
A gas generator can also be used when the valve can be controlled into more than two different positions. It is possible, with such a gas generator, to improve the triggering method of the gas generator according to the invention in that, optionally, a change takes place between several valve positions definable by the triggering. A better adaptation of the filling operation of the air bag to an accident can thereby be achieved.
In a further development of the process, gas generator triggering takes place such that the valve of the gas generator opens at a frequency defined by the control signal. After each opening of the valve, the latter remains open for a fixedly definable time period and, after expiration of this time period, the valve is closed again. The predeterminable time period, during which the valve remains open, must be shorter than a period length of the triggering frequency if the valve is not to be open continuously. The frequency for triggering the gas generator is determined by the control unit; an acceleration signal is utilized and the seriousness of an accident is derived therefrom. A frequency is assigned to the seriousness of an accident corresponding to a conversion function or a table, and the gas generator is triggered by this frequency. The triggering frequency is decisive for the filling operation of the air bag. It is an advantage of this further development of the process that, as a result of an assignment of the seriousness of an accident to a frequency, a simple criterion is defined for triggering the gas generator by which the filling operation of the air bag can be adapted in a continuous manner.
Evaluation of the acceleration signal for triggering the valve takes place such that an average acceleration is determined. Determination of the average acceleration can take place, for example, by simply taking the mean of the acceleration signal with respect to the time. As an alternative, the average acceleration is determined from the speed change. The speed change is computed by integration of the acceleration signal and is a frequently used quantity for determining the seriousness of an accident. The slope of the speed change curve, when representing the speed change as a function of time, corresponds to acceleration. A linear regression of the speed change curve corresponds to an average acceleration. By way of the average acceleration, a parameter is used for triggering the gas generator which permits good differentiation between various degrees of seriousness of an accident. The advantage of this further development of the method is the fact that only a linear regression has to be carried out for evaluating the speed change.
In an alternative further development, the method can be implemented by way of a gas generator which, instead of a controllable valve, has a reactant which can be ignited in discrete steps. For example, a discrete arrangement of combustible pellets can be provided with respective triggerable ignitors so that each combustible pellet can be ignited individually.
As a further development of the method, a voltage signal is assigned to the determined average acceleration, which voltage signal relates the acceleration to a voltage. By way of a voltage/frequency converter, the frequency for triggering the gas generator is produced from the voltage signal. Thus, the frequency for triggering the gas generator can be generated in a simple manner.
In addition to the adaptation of the filling operation of the air bag to the detected seriousness of an accident, by way of the method according to the invention, an adaptation of the filling operation to the occupants of a vehicle, for example, to their heights, weights and positions, can also take place. Driving-dynamic quantities, such as the weight of the vehicle itself, and environmental quantities, such as the differential speed between the vehicle and a collision object, can be used as additional parameters for controlling the gas generator. In situations in which an occupant may be endangered by the filling of the air bag, triggering of the gas generator may be changed such that the risk of an injury arising because of air bag inflation is considerably reduced.
In a method according to the invention for triggering a gas generator, a correction of the preceding accident evaluation is possible because the filling operation can still be changed during the filling operation. The decision concerning the seriousness of an accident can therefore be made with a certain fuzziness, whereby an early decision is permitted. This permits an early filling of the air bag, whereby its protective effect is increased and the stress to the occupants caused by the air bag is simultaneously reduced.